The present invention relates to a voltage monitoring device for monitoring voltage of a primary-side circuit from a secondary-side circuit or monitoring voltage of the secondary-side circuit from the primary-side circuit while maintaining electric insulation between the primary-side and secondary-side circuits, which have different voltages, and to an inverter device.
There are electric devices provided with a primary-side circuit and a secondary-side circuit having different voltages. A semiconductor such as a photocoupler or an electromagnetic component such as a transformer are used to maintain electric insulation between the primary-side and secondary-side circuits when monitoring the primary-side voltage from the secondary-side or monitoring the secondary-side voltage from the primary-side.
Japanese Laid-Open Patent Publication 5-68338, for example, describes an electronic device incorporating a remote-controllable power supply unit that maintains the electric insulation between a circuit connected to the primary-side of the power supply unit and a circuit connected to the secondary-side of the power supply unit. The electronic device is provided with a power supply unit for generating DC voltage from a commercial AC power supply. The power supply unit has a remote control circuit located at its primary-side. The remote control circuit performs remote control based on an external control signal indicating whether or not DC voltage is output from the secondary-side. An electronic circuit and a system control circuit, which is operated by output voltage of the power supply unit, are arranged at the secondary-side of the power supply unit. Operation of the electronic circuit is controlled by the remote control circuit and the system control circuit. A photocoupler is arranged in a signal transmission channel between the remote control circuit and the system control circuit to function as a means for insulating the two circuits.
Japanese Laid-Open Utility-Model Publication 5-55435 describes a status detection circuit for an output switch arranged in a load circuit. The opening and closing of the output switch is controlled by a control unit, which is insulated from the output switch. The status detection circuit includes an insulating transformer, the secondary-side of which is closed when the output switch opens the load circuit, an oscillation circuit, which applies an oscillation output to the primary-side of the insulating transformer, a current detection means, which detects the primary-side current of the insulating transformer, and a determination means, which determines whether the output switch is open or closed based on the current detected by the current detection means.
It is difficult to design a circuit without using an insulative component, such as a photocoupler or a transformer, to maintain electric insulation between a primary-side and secondary-side. However, the use of an insulative component, such as a photocoupler or transformer, increases costs.